commercetools / enzyme-extensions

@commercetools/enzyme-extensions

Why should you use this? Read: Test a Render Prop!

NOTE This package used to provide a renderProp test helper, which is now part of enzyme itself as of v3.8.0 🎈.

We therefore dropped renderProp in v4.0.0 of this package. We recommend to use renderProp from enzyme itself instead.

Be aware that the API has changed while moving the function to enzyme.

// before
wrapper.renderProp('foo', 10, 20);
// after
wrapper.renderProp('foo')(10, 20);

We are happy that our little helper has made it into enzyme.

What assumptions is this built with?

• We like to shallow render and avoid mounting
  • 🤺 Shallow rendering is fast and ensures that you only interact with the unit under test
  • 🏙 Shallow rendering ensures that you do not snapshot past your test's concern
  • 🏎 Shallow rendering has shown to be more performant for us than mounting
• We like declarative components and Render Props
  • 🧠 We can compose components easily while following along their interactions
  • 🔪 We like stubbing to test individual pieces of logic

Installation

1. Add package

yarn add @commercetools/enzyme-extensions -D

2. Add a test setup file (test runner dependent)

For Jest you would set up a setupTestFrameworkScriptFile. Create that file and add it to the jest configuration.

3. Extend Enzyme with this package's helpers

In that testFrameworkScriptFile file, import the extensions and add them to Enzyme

import Enzyme from 'enzyme';
import Adapter from 'enzyme-adapter-react-xx';
import configure from '@commercetools/enzyme-extensions';
import ShallowWrapper from 'enzyme/ShallowWrapper';

// You likely had this part already
Enzyme.configure({ adapter: new Adapter() });

// This is the actual integration.
// Behind the scenes this extends the prototype of the passed in `ShallowWrapper`
configure(ShallowWrapper);

Usage

Once set up, you can use the extension in your test files like this:

import React from 'react';
import { shallow } from 'enzyme';

describe('when rendering `<App>`', () => {
  const App = () => (
    <div id="app">
      <Mouse
        render={(x, y) => (
          <div>
            Cursor is at {x} {y}
          </div>
        )}
      />
    </div>
  );

  // Here we call the render function defined on Mouse and we provide
  // some custom arguments to it. This means we are effectively mocking
  // the Mouse component's implementation.
  // This is great to keep test concerns separate.
  const wrapper = shallow(<App />)
    .find(Mouse)
    // This is where we are actually using the drill function
    // Since we defined it on the prototype in the Installation step,
    // it does not need to be imported into the test itself.
    // We can call any property dynamically and even derive the property to
    // call depending on the props which are passed as the arguments of the
    // function passed to `drill`.
    .drill(props => props.render(10, 20));

  it('should render the mouse position', () => {
    expect(wrapper.equals(<div>Cursor is at 10 20</div>)).toBe(true);
  });
});

Enzyme's renderProp is built as an easy to use test helper for the most common cases. In case you need more control, you can use drill instead. drill offers more flexibility as:

• the prop-to-call can be derived from the other props
• the returned element can be set dynamically

See the drill documentation for more.

Documentation

• drill
• until